Ca(TeO)(MO) (M = Mo, W): Mid-Infrared Nonlinear Optical Tellurates with Ultrawide Transparency Ranges and Superhigh Laser-Induced Damage Thresholds.

Intense interests in mid-infrared (MIR) nonlinear optical (NLO) crystals have erupted in recent years due to the development of optoelectronic applications ranging from remote monitoring to molecular spectroscopy. Here, two polar crystals Ca(TeO)(MO) (M = Mo, W) were grown from TeO-MO flux by high-temperature solution methods. Ca(TeO)(MoO) and Ca(TeO)(WO) are isostructural, which feature novel structures consisting of asymmetric MO tetrahedra and TeO trigonal pyramids. Optical characterizations show that both crystals display ultrawide transparency ranges (279 nm to 5.78 μm and 290 nm to 5.62 μm), especially high optical transmittance over 80% in the important atmospheric transparent window of 3-5 μm, and superhigh laser damage thresholds (1.63 GW/cm and 1.50 GW/cm), 54.3 and 50 times larger than that of state-of-the-art MIR NLO AgGaS, respectively. Notably, they exhibit the widest band gaps and the loftiest laser-induced threshold damages among the reported tellurates so far. Moreover, Ca(TeO)(MO) exhibit type I phase matching at two working wavelengths owing to their large birefringence and strong second-harmonic generation responses from the distorted anions, as further elucidated by the first-principles calculations. The above characteristics indicate that Ca(TeO)(MO) crystals are high-performance MIR NLO materials, especially applying in high-power MIR laser operations.